Process of extracting zinc from ores



APPLICATION FILED IAN-5,1920.

Patented Dec. 14, 1920.

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UNITED STATES PATENT oFFlcE.

FREDERICK LAIST, OF ANACONDA, AND JAMES ORR ELTON, GREAT FALLS, MON- TANA, ASSIGNORS TO ANACONDA COPPER MINING COMPANY, OF ANACONDA, IVION-` TANA, A CORPORATION 0F MONTANA.

PROCESS OF EXTRACTING ZINC FROM ORES.

To all whom t may concern:

Be it known that we, FREDERICK LAIST and (2) 4JAMES ORR ELTON, citizens of the United States, residing at (1) Anaconda, (2) Great Falls, in the counties of (l) Deerlodge, (2) Cascade, and State of Montana, have invented certain new and useful Improvements in Processes of Extracting Zinc from Ores, of which the following is a specification.

The object of this invention is the provision of a cyclical process by which zinc may be economically extracted from ores in which it exists in association with other metals such as lead, iron, copper, silver, gold, etc.

F or the proper performance of the cycle thezinc should be present in the ore as oxid,

or as a mixture of oxid and sulfate, with as little sulfid as possible, the oxidation of sulid ores being preferably accomplished by roasting. Although any unroasted sulid maybe recovered by flotation of the leached residue, nevertheless it is desirable for the purposes of this invention to convertas great la proportion as possible of the sulid into oxid in the original roast.

The roasted ore or concentrate is treated with dilute sulfuric acid, the ore or concentrate being. in quantity sufficient not only to neutralize all of the acid, but also torinsure the precipitation of iron, arsenic, antimony, etc. Provision is made in accordance with the usual practice for the oxidation of the iron dissolved in the leach, as well as of any ferrous iron that may have been added to `the leach orto the leaching solution prior` to the leaching operation.

it is a well recognized fact that in a leach of the above character, where the gangue material of the ore contains silica in forms soluble in dilute sulfuric acid, a certain amount of silica will pass into solution and will remain in solution after Ineutralization, unless a suliicient excess of base, such as calcium carbonate or zinc oxid, is added to linsure its removal. When the silica is removed by means of calcium carbonate, filtration of the resulting residue is usually slow, and moreover the moisture content of the residue is high, making it desirable to dehydrate this residue in order to granulats the precipi' tated silica befpl' the final leachingand ltration.

Specification of Letters Patent. Patented Dec, 14, 1920,

Application filed January 5, 1920. Serial No. 349,575.

According to the present invention, an excess of zinc oxid is added, either in the form of roasted ore or pure zinc oxid, under conditions to precipitate the soluble silica in such form that it is practically insoluble in a second treatment with dilute acid, and moreover does not interfere seriously with the filtration. The amount of oxid or roasted ore necessary to be used is determined byl complete coagulation of the leach, as indicated by rapid settling after neutralization. Heat aids the reaction and reduces the quantity of zinc oxid required.

The neutral solution resulting fromthis leach is partly separated from the residue by settling, or by settling and filtration, and is sent to a purification system to be freed from the remaining impurities, such as copper, cadmium, etc., by the usual methods; and is later electrolyzed4 with lead or other in soluble anodes for the production of metallic zinc and the regeneration of dilute sulfuric acid. The dilute acid so regenerated is used again as the leaching solution. thereby completing the cycle.

The residue with the entrained solution derived from the neutral leach described above is treated with sufficient dilute sulfuric acid to dissolve all the material which is readily soluble in weak acid, and to provide sufficient acid in excess to insure .the presence of acid in contact with the residue up to the time of its final separation from the solution. After a sufficient period of agitation this acid pulp is sent to settlers and filters, or other suitable equipment for the separation of the residue and dilute acid solution. The residue so obtained is practically fred from soluble zinc by washing with water or dilute acid or both, and is then discarded in so far as the present process is concerned. The resulting solution, containing a small proportion of acid, is returned to the ore-leaching operation, where it becomes mixed with that'portion of the returned solution from the electrolytic cells that is used in the primary or neutral leach. In the leach of the residue from the primary leaching a certain amount of iron which has been precipitated in the primary leach is re-dissolved and is held in solution as ferricsulfate, and as compounds of iron with arsenic, antimony and other impurities."

` and as the apparent acid content is reduced for acid, using methyl orange as an cator, -ferric sulfate acts similarly to an acld, so that when the acid reaction dlsappea'rs,

the ferrie sulfate is found to be completely precipitated.V Therefore, instead" of` having free sulfuric acid present, the titration may be made With ferric sulfate solution alone,

increasing the (apparent) acid content of the zio final solution from the second leach. This is readily accomplished by diverting a greater portion of the acid solution from the electrolytic cells to the Asecond leach. This procedure affords a'n easy method of controlling the iron`content of the leaching solution,'and

effects a saving in the amount of iron necessary to be added in order to eliminate the arsenic and antimony lcontent of the solution.l Thereby We are able to conserve the soluble iron content of anV ore containing a 'low per cent. of iron and small amounts of arsenic, antimony, etc. If too much iron is being returned from the second leach to the primary leach, thisy is readily corrected by reducing the (apparent) acid content of the second leach, thereby precipitating a portionof the iron. M

The amount. of arsenic and antimony. redissolved in.. the second "leach seems to be roughly proportional to the volvume of solution handled through that leach. lt is.' ad.-

- visable, therefore, in general practice, to put as much solution through thefirst leach and as little through the second leach as pos-- sible, While so controlling and adjusting the distribution of the solutions as to obtain the desired results. In practical operation, as a general rule, We prefer,to'apply approximately four-fifths of the total acid solution to the'first leach, the balancebeing applied to the secondary leach; obviously, however, these proportions Will vary according to the particular ore treated.

The accompanying drawing is a diagrammatic How sheetI ofthe process in its preferred embodiment, illustrating the distribution of the acid liquor to the primary and secondary leaching operations.

following may be'mentionedz.

(l.) The elimination of limestone, milk of lime, or other foreign material-commonl maryleach; t y

(21) The elimination of drying andde;

primary residue before the secondary from its ores, comprising leaching leaching solution in the -primar leach by controlling the'v (apparent) aci ity ofthe second leach; v

The production of a v final residue which is easily filtered, low in moisture, and

low i'n the amountof undiss'olved zi nc solu-v ble in dilute sulfuric acid;

(5L Removal of -the bulkof the solution efore the' secondary leach affords increased settling capacity in the equipment for the acid leach. settling system, or renders possible the reduction of this equipment; (6.) The temperature of the1 neutral leach is kept at a maximum by the rapid addition of all the roasted ore to the acid solution, the heat of reaction maintaining the temperature of the leach, and thereby'promot# ing settling;

(7.) 'The large bulk of the residue from the neutral leach materially aids in settling the precipitated iron, silica, etc. in the neutral settlers;

(8.) The precipitation of a portion of. the copper in the neutral solution bythe excess zinc oxid in the roasted ore-renders in this manner any remaining zinc sulfd. We claim 1; A cyclical process of extracting zinc the ore with dilute sulfuric acid in quantity insuficient for complete extraction of the zinc;

purifying the resulting zinc sulfate solution and `electrolyzing' the same with insoluble "anodes to produce metallic zinc and a dilute acid solution; vreturning -a portion of said acid 'solution tokftheprimary ore-leaching operation; and "applying another portion thereof to kleaching the residue from the primary leaching operation.

"the second leachif it is desired to recover 2. A cyclical process of extiacting `zinc from its ores, comprising leaching the ore withy ldilute sulfuric acid in quantity in# suiiicient for complete extraction of the zinc; purifying the resulting zinc sulfate solution and electrolyzing the Asame with insoluble anodes to producemetalliczinc and a dilute acid solution; returning aA portion of said acid -solution to vthe pri-1;

- mar ore-leaching operation; applying an- Among the advantages of the process, the y other. portion thereof to 'leaching the residue from th'e primary leaching operation; and returning tion to t employedfo'r the neutralization of the prlf, Y

the resulting zinc-bearing solue primary leaching operation.' 3; process of extracting zinc 'from Ores,. the steps comprising caching the vv fore with dilutesulfuric acid in `quantity inhydratmg, or'offlteringand drying, tige (3,?) Controlof the iron cmltelll" Q. ih

suiliciiant'for"completelextraction of the zinc, separating the" resulting. zinc sulfate v,solution hfom the zinc-bearing, Y:residue tannil sub-J jecting said residue to a secondary leaching operation With dilute sulfuric acid.

4. In a process of extracting zinc from its ores, the steps comprising leaching the ore With 'dilute' sulfuric acid in quantity insufficient for complete extraction of the zinc, separating the resulting zinc sulfate solution from the zinc-bearing residue, subjecting said residue to a secondary leaching operation With dilute sulfuric acid,' and returning the resulting zinc-bearing solution to the primary leaching operation. ln testimony whereof We aiiX our signatures.

FREDERICK LAIST. JAMES URB ELTON. 

